Oxides, hydroxides, or oxides such as a hydroxylated oxide are used in various fields; especially microparticles thereof are widely used in such fields as an abrading agent, a catalyst, cosmetics, an electronic apparatus, a magnetic substance, a pigment and a coating material, and a semiconductor.
Oxides, hydroxides, or oxides such as a hydroxylated oxide can improve their properties by making them microparticles; and these microparticles are produced generally by a sol-gel reaction or a sol-gel reaction followed by calcination as shown in Patent Document 1, and a hydrothermal reaction as shown in Patent Documents 2 and 3.
However, when general production methods as mentioned above are used, dispersion of oxide microparticles or hydroxide particles is poor in many cases; especially the oxide which is produced by calcination forms a bound agglomeration of primary particles so strongly that they are occasionally fused together. Because of this, when the oxides and the hydroxides thus produced are dispersed into various solvents or resins, they are dispersed often by mechanical grinding or mechanical crushing by using such machines as a ball mill and a bead mill. However, oxide particles in the oxide particle dispersion solution or hydroxide particles in the hydroxide particle dispersion solution, if these particles are produced, by the foregoing methods, had problems of not expressing expected semiconductor properties, transparency, spectroscopic properties, durability, and so forth, because there is a strong force acting on particles (crystals).
Applicant of the present invention provided, as shown in Patent Document 4, a method to produce oxide microparticles wherein the microparticles are separated in a thin film fluid which is passing between processing surfaces which are disposed in a position they are faced with each other; but a method to produce oxide microparticles having improved dispersibility has not been disclosed specifically. Accordingly, a method to produce oxide microparticles or hydroxide microparticles having improved dispersibility has been eagerly wanted.